//===- LazyBlockFrequencyInfo.h - Lazy Block Frequency Analysis -*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This is an alternative analysis pass to BlockFrequencyInfoWrapperPass.  The
// difference is that with this pass the block frequencies are not computed when
// the analysis pass is executed but rather when the BFI results is explicitly
// requested by the analysis client.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
#define LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H

#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Pass.h"

namespace llvm {
class AnalysisUsage;
class BranchProbabilityInfo;
class Function;
class LoopInfo;

/// \brief This is an alternative analysis pass to
/// BlockFrequencyInfoWrapperPass.  The difference is that with this pass the
/// block frequencies are not computed when the analysis pass is executed but
/// rather when the BFI results is explicitly requested by the analysis client.
///
/// There are some additional requirements for any client pass that wants to use
/// the analysis:
///
/// 1. The pass needs to initialize dependent passes with:
///
///   INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
///
/// 2. Similarly, getAnalysisUsage should call:
///
///   LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU)
///
/// 3. The computed BFI should be requested with
///    getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() before either LoopInfo
///    or BPI could be invalidated for example by changing the CFG.
///
/// Note that it is expected that we wouldn't need this functionality for the
/// new PM since with the new PM, analyses are executed on demand.
class LazyBlockFrequencyInfoPass : public FunctionPass {

  /// Wraps a BFI to allow lazy computation of the block frequencies.
  ///
  /// A pass that only conditionally uses BFI can uncondtionally require the
  /// analysis without paying for the overhead if BFI doesn't end up being used.
  class LazyBlockFrequencyInfo {
  public:
    LazyBlockFrequencyInfo()
        : Calculated(false), F(nullptr), BPI(nullptr), LI(nullptr) {}

    /// Set up the per-function input.
    void setAnalysis(const Function *F, const BranchProbabilityInfo *BPI,
                     const LoopInfo *LI) {
      this->F = F;
      this->BPI = BPI;
      this->LI = LI;
    }

    /// Retrieve the BFI with the block frequencies computed.
    BlockFrequencyInfo &getCalculated() {
      if (!Calculated) {
        assert(F && BPI && LI && "call setAnalysis");
        BFI.calculate(*F, *BPI, *LI);
        Calculated = true;
      }
      return BFI;
    }

    const BlockFrequencyInfo &getCalculated() const {
      return const_cast<LazyBlockFrequencyInfo *>(this)->getCalculated();
    }

    void releaseMemory() {
      BFI.releaseMemory();
      Calculated = false;
      setAnalysis(nullptr, nullptr, nullptr);
    }

  private:
    BlockFrequencyInfo BFI;
    bool Calculated;
    const Function *F;
    const BranchProbabilityInfo *BPI;
    const LoopInfo *LI;
  };

  LazyBlockFrequencyInfo LBFI;

public:
  static char ID;

  LazyBlockFrequencyInfoPass();

  /// \brief Compute and return the block frequencies.
  BlockFrequencyInfo &getBFI() { return LBFI.getCalculated(); }

  /// \brief Compute and return the block frequencies.
  const BlockFrequencyInfo &getBFI() const { return LBFI.getCalculated(); }

  void getAnalysisUsage(AnalysisUsage &AU) const override;

  /// Helper for client passes to set up the analysis usage on behalf of this
  /// pass.
  static void getLazyBFIAnalysisUsage(AnalysisUsage &AU);

  bool runOnFunction(Function &F) override;
  void releaseMemory() override;
  void print(raw_ostream &OS, const Module *M) const override;
};

/// \brief Helper for client passes to initialize dependent passes for LBFI.
void initializeLazyBFIPassPass(PassRegistry &Registry);
}
#endif
